1. Field of the invention
The present invention is generally concerned with contour reading devices adapted to "read" any shape and it is more particularly directed to the case where it is a question of establishing the specific contour of the rings or surrounds of an eyeglass frame in order to trim ophthalmic lenses to be fitted into the frame.
2. Description of the prior art
Generally speaking, the contour reading devices usually employed to this end comprise a carriage which, carrying a feeler designed to be applied to the article whose contour is to be read and thus in this instance adapted to be applied against the bottom of the bezel of the ring or surround of the eyeglass frame concerned, is able to move relative to the eyeglass frame in a system of polar or Cartesian coordinates, for example.
In European patent application No 0 181 788, for example, in an arrangement that is known in itself, the carriage is mounted for passive to-and-fro movement on a guide, controlled by a simple return spring.
There are two particular problems to be overcome in producing contour reading devices of this type.
The first concerns the fact that, although it has to be able to move, the carriage has to apply the feeler that it carries against the ring or surround of the eyeglass frame concerned with a controlled and strictly defined force, failing which the feeler could deform the ring or surround and compromise the accuracy of the measurement.
The second concerns the fact that when the ring or surround concerned comprises localized areas where the curvature varies quickly, as is the case with half-moon or water droplet shape ophthalmic lenses, for example, it is not rare for the feeler to become jammed in such areas.
A general object of the present invention is an arrangement whereby these problems can be overcome.